Evolving mobile cellular standards such as Global System for Mobile Communications (GSM) and Wideband Code Division Multiple Access (WCDMA) will likely require modulation techniques such as OFDM in order to deliver higher data rates. OFDM is a method for multiplexing signals which divides the available bandwidth into a series of frequencies known as carriers. OFDM is somewhat immune to inter-symbol interference (ISI) because its symbol duration is longer than the symbol duration in single-carrier modulation techniques such as CDMA and TDMA. To further reduce ISI, guard periods are appended to the OFDM symbol. The guard periods may be comprised of a cyclic prefix of the OFDM symbol. Introducing cyclic prefix in OFDM makes OFDM robust against delay spread and facilitates comparatively higher data rates.
In order to ensure a smooth migration from existing cellular systems to high capacity, high data rate systems using existing radio spectrum, new systems must be able to operate on a flexible bandwidth (BW). Super third generation (S3G) has been proposed as a new flexible cellular system. S3G is intended as an evolution of the 3G WCDMA standard supporting only packet data services. S3G will likely use OFDM and operate on BWs spanning from 1.25 MHz to 20 MHz. Data rates of up to 100 Mb/s will be possible in the high bandwidth S3G service. In order to achieve such high data rates, the latency or round-trip time (RTT) must be below 10 milliseconds (ms). RTT is the time taken for a packet of data to travel across the network with an acknowledgement sent back to the transmitter. Hence, it is expected that transmission time intervals (TTIs), which are the length of a coded block, will be about 0.5 ms.
S3G's flexibility, short RTT and high data rates will present additional complexity to mobile terminal design. For example, packet paging detection must occur quickly in order to have a power efficient mobile terminal implementation that is adapted to quickly switch between the on state and sleep state. In other words, user equipment (UE) must be designed to have a low duty cycle even in a 0.5 ms TTI case. The duty cycle is the relative amount of time the radio is turned on. A low duty cycle means that the radio is turned on for a short duration of time compared to the time when it is turned off.
FIG. 1 shows a proposed S3G TTI of 0.5 ms. The time duration of each TTI is always the same but the number of OFDM symbols can vary from 6-8 depending of the size of the cyclic prefix. In cells where a large cyclic prefix is needed, there are fewer OFDM-symbols compared to cells with a small delay spread. As seen in FIG. 1, the OFDM symbols include paging information 101, other control information 102 such as broadcast and synchronization information, and data 103. The paging information 101 is incorporated in the first OFDM symbol. Since paging information 101 typically consists of 10-100 bits and each OFDM symbol consists of 4800 bits, based on a 20 MHz BW, with 1200 carriers and 16 Quadrature Amplitude Modulation (QAM), only a very small fraction of the first symbol consists of paging information. In order to have some frequency diversity, the paging information is spread out, for example over 1 MHz. This is still a much smaller BW compared to the total BW, for example, up to 20 MHz.
In a conventional method of paging detection, paging information is first sent to the UE and then the non-paging data is sent. In order to save as much power at the terminal or UE as possible, the radio and baseband processor in the UE should be turned off if it is not needed. What is desired is a method and apparatus for detecting paging information more efficiently in a wide BW, high data rate S3G implementation. Such a method and apparatus would send paging information and non-paging data at the same time. Such a method and apparatus would reduce the duty cycle and thereby reduce UE power consumption.